IMPROVED ZERO-CURRENT TRANSITION CONVERTERS FOR HIGH-POWER APPLICATIONS

Existing zero-current transition (ZCT) converters do not solve main sw itch turn-on problems and require auxiliary switches to be turned off with high current and, therefore, are not suitable for high-power appl ications, Novel ZCT schemes proposed in this paper enable all main swi tches and auxiliary switches to be turned on and off under zero-curren t conditions, The zero-current switching at both turn-on and turnoff n ot only reduces switching losses significantly, but also eliminates th e need for passive snubbers, due to the much reduced switch stress. Th e cost of the auxiliary switches can be reduced compared to the existi ng ZCT schemes, due to their zero-current turnoff. The proposed techno logy is well suited for de-de and three-phase converters with insulate d gate bipolar transistors (IGBT's), MOS-controlled thyristors (MCT's) , and gate-turnoff switches (GTO's), Theoretical analysis, computer si mulation, and experimental results are presented to explain the propos ed schemes.